Disclosed herein are a method and an apparatus for inspecting empty containers for contaminants, with a radiation source for generating an exciting radiation, wherein the exciting radiation is directed on to the inner wall of an empty container and there excites contaminants to be detected in such a way that they emit luminescent radiation, with at least one device for detecting the luminescent radiation emitted by the contaminants and with a device for analysing the detected luminescent radiation.
The present disclosure is intended in particular for use in automatic filling systems in which the containers are transported at high speeds of up to 90,000 bottles per hour. To avoid any negative effect on the throughput of such bottle filling systems, the inspection devices for monitoring the containers must also be designed to inspect the containers at high speeds.
In automatic filling systems, empty containers are examined for possible contaminants or foreign bodies before being filled. Conventionally, this involves passing the containers through an inspection device which comprises a light source for visible light and a CCD camera. This substantially involves shining light through the containers and inspecting them from various viewing angles so that a reliable detection of contaminants is ensured. Such an inspection device is known e.g. from EP 0 415 154 A1.
It has been shown that, with conventional inspection devices, certain contaminants, in particular organic contaminants such as mould fungi, fats, hydrocarbons, insect larvae, microbes or plastics, are very difficult or even impossible to detect with such inspection devices.
Furthermore, it is known that some, in particular organic, contaminants exhibit luminescence phenomena, i.e. that, by the action of energy from an external source, they can be shifted into excited states and can then return to the ground state by emitting luminescent radiation. The various types of luminescence are categorized here according to the duration of the glow after the excitation has ended. Fluorescence denotes a very brief afterglow occurring as a direct consequence of and a concomitant phenomenon to the excitation. The term phosphorescence describes a longer afterglow lasting longer than 1 ms after the excitation has ended.
The excitation generally takes place here by irradiation with UV light. UV light is not conventionally used for inspecting containers since container glass in particular has very low or even no transparency to UV light.
From WO 2008/092537 A1, an apparatus for the optical characterization of sample material is known, wherein inter alia UV light is employed. At least one UV detector is provided, with which the fluorescence or luminescence of the sample can be determined. Since the illumination of the sample takes place from outside through the container wall, this must be transparent to the radiation used.
From DE 10 2010 043 131 B1, an apparatus for the contactless investigation of a property of the contents of a container by means of electromagnetic radiation is known. The container can be for example a grain silo, a fermentation tank or a similar container and the apparatus is used to carry out a contactless measurement to monitor the progress of the process of the contents located in the container. Since the penetration depth of the radiation can be relatively low, a device is provided with which a medium is streamed into the container in order to create a vortex in the interior of the container. The medium causing the vortex in this case is transparent to electromagnetic radiation, so that in the interior of the vortex a contactless measurement can be performed to determine a property of the contents of the container.